The present invention relates, in general, to a clutch release bearing, and more particularly to a clutch release bearing for use in a clutch mechanism for motor vehicles.
A clutch release bearing is typically intended for actuation of a clutch mechanism, e.g. separating clutch, disposed between the internal combustion engine and a gearbox, and is configured as a tapered roller bearing which includes a revolving outer bearing ring, a non-rotatable inner bearing ring, and rolling members, received in a cage and guided between the bearing rings. Supported against the outer ring is an adjustment ring, which establishes a connection between a disk spring of the clutch mechanism and the release bearing, whereby the disk spring bears directly on a skirt of the outer ring at the side of the adjustment ring confronting the clutch mechanism. The adjustment ring is configured to allow a relative movement of the adjustment ring and the outer ring so as to implement a self-adjusting or self-aligning release bearing.
Such a release bearing is able to compensate shocks generated by axial misalignment with the disk spring that is connected directly to the clutch mechanism. The axial shocks, caused by the disk spring and reinforced by the operation of the internal combustion engine, increase wear and thus reduce the service life of the release bearing.
German Pat. No. 199 12 432 A1 describes a release bearing with a revolving outer ring for direct support of an adjustment ring. In their contact zone, the outer ring and the adjustment ring have complementary calotte-shaped segments to allow a relative movement. The outer ring of the release bearing as well as the adjustment ring are made of steel. As a consequence, rust formation caused by friction can be experienced, resulting in greater wear. High wear results in annoying noise and triggers the so-called clutch judder that adversely affects the overall riding comfort, so that the service life of these release bearings is insufficient to meet the demands by vehicle manufactures.
It would therefore be desirable and advantageous to provide an improved release bearing, which obviates prior art shortcomings and which exhibits a long service life, is maintenance-free and inhibits noise while still being reliable in operation and cost-efficient to produce.
According to one aspect of the present invention, a release bearing includes a rolling-contact bearing having a non-rotatable inner ring, a rotating outer ring, and plural rolling members located between the inner and outer rings; an adjustment ring having a ring flange for abutment against a disk spring of a clutch mechanism; and a sliding element made of bearing material and disposed in a support zone, which is defined between complementary calotte-shaped portions of the outer ring and the adjustment ring so that the adjustment ring and the outer ring are movable relative to one another for effecting a self-adjustment of the release bearing.
The present invention resolves prior art problems by providing a sliding element in the support zone or contact zone between the adjustment ring and the revolving outer ring of the release bearing. The sliding element is suitably made of a bearing material or appropriate friction-reducing and wear-resistant material which is maintenance-free to ensure a long service life. As a result of the reduction in friction, the self-adjusting feature of the components, outer ring and adjustment ring, is significantly improved. The optimized self-adjustment is further able to significantly dampen the axial shocks transmitted via the clutch mechanism into the release bearing. The provision of a sliding element eliminates a direct contact of the steel parts, adjustment ring and outer ring, and this prevents friction-based rust formation. By sandwiching the sliding element in the support zone between the outer ring and adjustment ring, the latter components are effectively decoupled from one another so that noise development is suppressed. A direct contact of the adjustment ring upon the outer ring is suitably avoided to thereby ensure a maintenance-free, low friction and sat the same time damping self-adjustment between the mutually moving components, adjustment ring and outer ring. The sliding element can be connected to either one of the carriers, i.e. outer ring or adjustment ring, without requiring any modification of the carrier that is selected to bear against the sliding element, so that existing installation space can be used. Support of the adjustment ring on the outer ring permanently eliminates friction-based rust formation.
It is to be understood by persons skilled in the art that the term xe2x80x9ccarrierxe2x80x9d used in the description to refer to the outer ring or to the adjustment ring of the release bearing.
Wear of the spherical or calotte-shaped portions in the support zone between the sliding element and the outer ring or adjustment ring is significantly reduced compared to conventional self-adjusting release bearings. Moreover, clutch judder is effectively prevented which has a positive effect to reduce noise development. A sliding element according to the present invention can be fabricated in great numbers and does not require special handling for installation or securement to the adjustment ring or outer ring of the release bearing.
According to one embodiment of the present invention, the sliding element may be connected to the outer ring of the release bearing. A largest possible contact surface can be realized, when the sliding element embraces the entire side of the outer ring and is extended to an area shy of the contour of the non-rotatable inner ring at formation of a slight annular gap. In this way, the rotating outer ring can be optimized with respect to size and weight and may have a width which is substantially limited to the provision of a suitable raceway for the rolling members. At the same time, the sliding element ensures on the side confronting the adjustment ring a large contact zone or enlarged support zone for the adjustment ring. Thus, a sufficiently large contact zone or support zone between the mutually movable components is realized even at extremely tilted positions. As an alternative, the sliding element may also be connected directly to the adjustment ring to form a unitary structure which has calotte-shaped portions to complement the outer contour of the rotating outer ring of the release bearing. In either case, the large-area contact of the sliding element upon the adjustment ring or outer ring results in a sufficient support in each and every position, i.e., also when the adjustment ring occupies an extremely tilted disposition. At the same time, the large-area contact of the sliding element ensures a reduced surface pressure so that the strength and rigidity of the sliding element is not adversely affected.
According to another feature of the present invention, the sliding element may also be configured in segments, instead of a continuous contact, for resting upon the outer ring or adjustment ring. In this way, the adhesion of the sliding element is improved because tension as a consequence of different coefficients of thermal expansion between the different materials of the adjustment ring or outer ring, and the sliding element is effectively eliminated. Of course, the sliding element may also be configured with a longitude slot or groove, which coincides with the symmetry axis, in order to compensate varying coefficients of thermal expansion. Instead of one slot or groove, also several slots or grooves may be provided about the circumference of the sliding element and formed alternately on the inside or outside of the sliding element or extend through the wall of the sliding element. Any suitable configuration of the slot or slots is conceivable, i.e., straight, meander-shaped or slanted.
The production costs for making a sliding element according to the present invention can be reduced, when employing an injection molding process. This process can also be used to incorporate in a single step the slots and grooves in the sliding element for compensation of varying coefficients of thermal expansion.
Regardless of its configuration, the sliding element may be positively secured to either one of the carriers, i.e. outer ring or the adjustment ring of the release bearing. Suitably, the surface of the carrier may be formed with grooves for engagement or guidance of projections of the sliding element. As a result, the sliding element is also secured against rotation with respect to the carrier. As an alternative or in addition to the positive securement, the sliding element may also be urged into forced engagement with the carrier, for example, through gluing. An example of a suitable glue includes a high-temperature adhesive. Gluing of the sliding element ensures also a compensation of even small unevenness between the carrier and the sliding element so as to prevent the formation of voids which are detrimental to a secure attachment of the sliding element.
According to another feature of the present invention, the sliding element may be formed by a coating applied directly through injection onto the outer ring or adjustment ring. In this way, diametrical tolerances of the mating components, outer ring and adjustment ring, that may influence the structural length, are eliminated. Suitably, the carrier may include in the contact zone with the sliding element a circumferential crease or groove, which is filled by the material of the sliding element during injection molding, to realize an effective positive securement of the sliding element to the carrier and to prevent a rotation. Stress through shrinkage during injection molding can be counteracted in a controlled manner, by providing the outer ring or the adjustment ring in the support zone with at least one axis-parallel or helical notch. To prevent a rotation of the parts, a groove is provided in diametric opposition to the notch at the diameter and/or in the plane surface of the adjustment ring or outer ring and can also be filled with sliding element material during injection molding.
The sliding element, on the one hand, and the outer ring or the adjustment ring, on the other hand, may be made of different materials. The material for the sliding element is selected by taking into account optimum wear properties and friction properties as well as inexpensive fabrication and mounting to the outer ring or adjustment ring. The carrier, outer ring or adjustment ring, is suitably made of steel. The configuration of the carrier allows hereby a production without material removal, in particular a deep-drawing process that enables a production of the adjustment ring as well as of the outer ring on a large scale in a cost-efficient manner. To realize sufficient strength, especially wear-resistance, the adjustment ring as well as the outer ring may be heat-treated at least in those zones that are subject to high loads, such as the calotte-shaped segments, tracks for the rolling members, as well as the contact surface for support of the disk spring of the clutch mechanism.
The sliding element may suitably be made of a high-strength and wear-resistant plastic, such as thermoplastic material or a duroplastic material. The sliding element may include additives such as carbon fibers, MoS2 fractions, and/or epoxy resins, alone or in combination, for realizing a lubrication and/or improved service life, when the sliding element is based on duroplastic material. The use of duroplastic material significantly enhances the useful life of the sliding element, without adversely affecting the manufacturing costs. The sliding element may also be made of PPA or PA46 combined with carbon fibers as wear-reducing agent and PTFE as friction-reducing agent. Its may also be conceivable to make the sliding element of ceramic material. This ceramic material, also called industrial ceramic, exhibits optimal wear-resistance and is therefore suitable for use with a contact surface that is subject to severe conditions and soiling during operation of the release bearing.
Persons skilled in the art will understand, that the foregoing description of materials for the sliding element is not exhaustive but only illustrative, because other materials or material combinations may be conceivable as well so long as they generally follow the concepts outlined here, i.e. exhibit sufficient friction properties and wear-resistance and can be shaped appropriately and manufactured in a cost-efficient manner.
The adjustment ring may be made by a deep-drawing process and is suitably made of steel C80M which subsequently can be hardened through heat-treatment to realize an improved wear resistance.
According to another embodiment of the present invention that optimizes the number of used components includes an adjustment ring which is supported directly by the outer ring. Hereby, these structural parts form in a contact zone or support zone complementary calotte-shaped portions. An adjustment ring of this type can then suitably combined with a sliding element made from a duroplastic material by an injection tool drawn in axial direction to provide a N-section profile. The use of duroplastic material is advantageous here because of its sufficient strength and shape stability. The sliding element may be secured to the ring flange through gluing, in combination with protrusions of the sliding element for positive engagement in respective recesses of the ring flange.
According to another feature of the present invention, the adjustment ring may also be so configured that its components, ring flange and sliding element, are made of same material. For example, the adjustment ring may be made of ceramic material or duroplastic material. The components of the adjustment ring may be glued for realizing a permanent connection. Gluing may be assisted by a positive connection in which the sliding element is connected to the ring flange via a crown gearing and/or spline profiles or the like, whereby a greater contact surface is realized at the same time. In addition, the adjustment ring is secured against rotation and the bonding of the parts is improved. Excess glue can be accumulated in depressions or notches formed on at least one bonded surface of the mating annular regions being joined.
According to another feature of the present invention, that optimizes the number of used components includes a single-piece adjustment ring which is made exclusively of duroplastic material or ceramic and combined with the release bearing. An adjustment ring of this type corresponds also to an assembled adjustment ring, which has components made of same material.
According to another feature of the present invention, the release bearing may include a captivating mechanism by which all components of the release bearing are captivated after mounting and installation. Hereby, the rotating outer ring is provided with a sleeve or clip which extends axially over a contact zone of the adjustment ring with the outer ring. The sleeve or the clip is hereby spaced from the adjustment ring and guided while maintaining an annular gap. An end portion of the sleeve projects behind a marginal area, so that the release bearing including the adjustment ring is captivated to form a unitary structure.
According to another feature of the present invention, the calotte-shaped portions of the outer ring and the adjustment ring are disposed at an angle of xe2x89xa715xc2x0 to an axis of symmetry of the release bearing. Suitably, the sliding element and the outer ring or the adjustment ring have a radius of xe2x89xa730 mm in an area of the support zone.